Flotation cell



FLOTA'I'ION CELL Filed Feb. 5, 1941 2 Sheets-Sheet 2 ATTORNEY;

Patented July 13, 1943 FLOTATION CELL Louis Steffen Petersen, Forest Hills, N. 35., as-

signor to F. L. Smidth & Co., New York, N. Y., a corporation of New Jersey Application February 5, 1941, Serial No. 377,467 In Great Britain February 2'7, 1940 14 Claims.

This invention relates to apparatus for use in flotation operations in which constituents of various materials are separated from one another by preferential froth flotation. More particularly, the invention is concerned with a novel flotation cell which is superior to similar cells as heretofore constructed in that the parts thereof are not subjected to rapid and uneven wear and the cell can, accordingly, be employed for long periods without interruption for repairs or replacement of parts.

Flotation cells as now commonly constructed comprise a tank containing a rotor mounted on a vertical axis concentrically within a stator and driven at high speed. Air is introduced into the tank close to its bottom or top so that the pulp in the tank is intimately mixed with the air by the cooperation of the rotor and stator. The air may be introduced under pressure through the bot tom of the tank but frequently the rotor shaft is made hollow and air is drawn in through the shaft by the partial vacuum set up by the rotor.

It has been found that in the use of such cells, the stator wears unevenly and has to be removed from time to time for repair or replacement. Whenever this occurs, flow through the cell must be stopped, and that cell, as well as all others in direct series with it, must be emptied. Shut-downs for repairs or replacements upset the balance of the flotation system and it usually takes some time to bring a system back into balance. In many industries in which flotation is employed, as, for example, in the cement industry, a prolonged stoppage of the flotation equipment is likely to necessitate the shutting down of apparatus employed for the treatment of a product of the flotation operation. Accordingly, interruptions in the operation of the flotation'equipment may interfere with subseouent operations and may reduce the efficiency of the plant as a whole and result in substantial loss.

The present invention is, accordingly, directed to the provision of a flotation cell in which the parts submerged in the pulp wear evenly so that the cell may be employed uninterruptedly for long periods, and when such parts do need repair orreplacement they can be repaired or replaced without emptying the cell, or shutting down the other cells, or disturbing the condition of balance of the flotation system. In the cell, the agitation of the pulp is effected by the use of two rotors which are mounted concentrically and driven differentiaily, that is, at different speeds in the same direction or in opposite directions. Preferably, one rotor is mounted on a substantially vertical shaft and the other on a hollow shaft outside the first, the annular space between the shafts being then used for the introduction of air into pulp.

The rotors may advantageously be driven by one motorthrough two sets of driving connections, such as gears, and, preferably, the upper ends of the rotor shafts extend into a gear box which may be directly connected to the casing of the motor. The motor, gear box, and rotor assembly thus constitute a single unit which is mounted on a suitable support above the cell and can be quickly removed for repairs and replaced.

For a better understanding of the invention, reference may be made to the accompanying drawings in which Figure 1 is a view partly in elevation and partly in vertical section of one form of cell constructed in accordance with the invention; i

Fig. 2 is a sectional view on the line 2--2 0 Fig. 1;

Figure 3 is a view similar to Figure 1 of a modi- I fled construction;

Figure 4 is a sectional view on the line 4-4 of Figure 3;

Figure 5 is a fragmentary sectional view of another modiiled construction; and

Figure 6 is a sectional view on the line 66 of Figure 5.

The machine in the form illustrated in Figures 1 and 2 comprises a tank l0 of any suitable construction across thetop of which are supporting members H illustrated as beams. Mounted on the support is a motor [2, to the casing of which is attached a gear box l3 of conventional construction and containing two sets of gears. A hollow vertical shaft I4 extends down from the gear box into the tank and the upper end of the shaft is mounted for rotation in suitable bearings within the box and is driven through one of the sets of gears. A shaft I5 is mounted within the hollow shaft I4 concentrically therewith, and the upper end of shaft i5 is mounted in suitable bearings within the gear box and is driven by the other setof gears.

The inner shaft l5 carries a rotor of the impeller type at its lower end and this rotor comprises a plate IS on the upper face of which are mounted a plurality of upwardly extending cylindrical staves ll. A similar rotor consisting of a plate i8 and a series of downwardly projecting cylindrical staves i9 is secured to the lower end of shaft H. The plate i 8 is of greater diameter than the plate l6 so that the staves [9 lie outside the rim of the plate ii. The shaft [4 is provided with openings 20 and, when the rotors are rotated, the pulp in the tank is circulated, as indicated by the arrows. The shaft H is open at its upper end and the action of the rotors creates a partial vacuum and causes air to be drawn down through the hollow shaft and into the tank. Flotation takes place within the tank in the usual way.

The tank illustrated in Figures 1 and 2 is of the discontinuous type, but the rotor mechanism may be employed, if desired, in a continuous type of machine which includes the usual feed pipe, discharge, and skimmers.

In the construction shown in Figure 1, the motor i 2, gear box [3, and the rotor assemblies consisting of shafts I4 and I 5 and the inner and outer rotors at the lower ends thereof constitute a single unit and, should repair or replacement of the parts be necessary, the unit may be detached from the support and raised free of the tank. A new unit may then be quickly installed or, if circumstances permit, the unit removed can be repaired and replaced.

In the operation of the apparatus, the inner and outer rotors are driven differentially, as, for example, the outer shaft and outer rotor may be driven in the same direction as the inner shaft and its rotor but at at a slower speed. Instead, the shafts and their rotors may be driven at different speeds in opposite directions.

In that form of the machine illustrated in Figures 3 and 4, the inner rotor consists of upper and lower perforated plates or spiders 2| connected by staves 22. The rotor is mounted on a shaft 23 extending into the gear box 2| and driven by a set of gears therein which are. in turn, driven by the motor 25. A hollow shaft 28 encircles the shaft 23 and to its lower end is secured a rotor consisting of upper and lower rings 21 connected by staves 28 arranged in a circular series. The lower ring 21 is preferably provided with a downwardly extending flange 29 and a scraper 30 is secured to the under surface of the ring.

At its upper end, the shaft 2! is secured to a plate ll having a central opening'provided with a cylindrical flange 32 which flts over a hollow shaft 33 extending downwardly from the gear box. The flange 32 is connected to shaft 33 by one or more bolts 34 which pass through regis tering openings in the flange and shaft. The flange is formed with several such openings arranged one above the other and by insertion of the bolts through selected openings in the flange. the shaft 26 may be set at different heights. In this manner, the annular opening between the lower edge of flange 29 and the inner wall of the tank can be varied to regulate the circulation in the tank.

The pulp to be treated is fed to the tank through a ipe and air is drawn into the hollow shaft 28 through suitable openings in plate II, the circulation through the rotors being indicated by the arrows. tank through the pipe 31 and the froth concentrate overflows the upper ed e of the tank and enters an annular channel II provided with an outlet 89. To facilitate the removal of the froth. one or more skimmers ll may be provided, these skimmers being secured to the hollow shaft 26 so as to be carried over the surface of the contents of the tank as the latter is rotated. The

- shaft 26 rotates slowly at an appropriate speed for the skimming, while the shaft 23 is rotated at a different speed in the same direction or is rotated in the opposite direction at a different The tailings leave the speed to produce the desired agitation. The froth overflowing the edge of the tank enters the channel 38 and the skimmers may be provided with blades 4i entering the channel to propel the froth therein toward the outlet 39.

The machine illustrated in Figures 5 and 6 differs from that shown in Figure 3 with respect to the rotors employed. In the Figure 5 machine, the inner rotor comprises a propeller 42 mounted on the inner shaft 43 and having a plurality of blades 44. The outer rotor comprises a generally conical plate 45 secured to the lower end of the outer shaft 46 and having a periphery of greater overall diameter than the propeller 42. The inner and outer rotors are rotated diflerentially and the outer rotor is provided with a scraper 41 which sweeps over the inner surface of the lower part of the tank to keep it free from deposits. The pulp is introduced into the machine through a pipe 48 and the outer shaft 46 is provided with openings 40 through whichthe contents of the tank are drawn by the action of the propeller so that circulation is set up, as indicated by the arrows.

In all forms of the machine, the agitation of the pulp is effected by the use of inner and outer rotors driven differentially and with this construction, the wear on the rotors is even, whereas in similar machines in which there is a rotor and stator, the stator wears unevenly and requires relatively frequent repair or replacement. .In the machines illustrated in Figures 3 to 6, inclusive, the tanks are circular in cross-section, but, if desired, oblong tanks may be employed and one or more pairs of concentric rotors may be used. In each form of the apparatus shown, the air required is drawn in through the hollow shaft, but this is not essential and the air may be introduced through noczles in the bottom of the tank, if desired. Also. the material may be fed into the tank through the hollow shaft instead of through a supply pipe, as shown.

Iclaim:

1. Apparatus for froth flotation which comprises a tank having a solid bottom which. is directly exposed to thcinterior of the tank and on which solids may collect, a pair of rotors mounted for rotation on the same vertical axis within the tank, at least one of said rotors lying close to the bottom of the tank, and means for rotating the rotors at different speeds.

2. Apparatus for froth flotation which comprises a tank having a solid bottom which is directly exposed to the interior of the tank and on which solids may collect, a pair of concentric.

tom of the tank, and means for rotating th rotors at different speeds.

3. Apparatus for froth notation which oomprises a tank having a solid bottom which is directly exposed to the interior of the tank and on which solids may collect, a pair of rotors mounted for rotation on the same vertical axis withm the which solids may collect, a pair of rotors mounted for rotation on the same vertical axis within the tank, onerotor having a periphery of greater overall diameter than the other and at least one rotor lying close to the bottom of the tank, and means for driving the first rotor at a slower speed than the second.

5. Apparatus for froth flotation which comprises a tank having a solid bottom which is directly exposed to the interior of the tank and on which solids may collect, a pair of rotors mounted for rotation on the same vertical axis within the tank, one rotor lying within the other and at least one rotor lying close to the bottom of the tank, and means for rotating the rotors at different speeds.

6. Apparatus for froth flotation which comprises a tank having a solid bottom which is directly exposed to the interior of the tank and on which solids may collect, inner and outer rotors mounted for rotation within the tank on the same vertical axis, a member attached to the outer rotor and terminating close to the bottom of the tank, said member sweeping over said bottom to prevent the accumulation of solids there on, and means for rotating the rotors at diflerent speeds.

7'. Apparatus for froth flotation which comprises a tank, inner and outer rotors mounted for rotation within the tank on the same vertical axis, a member attached to the outer rotor to propel froth on top of the contents of the tank outwardly over the edge of the latter, and means for rotating the rotors at different speeds.

8. Apparatus for froth flotation which comprises a tank circular in cross-section, inner and outer rotors mounted for rotation within the tank on the same Vertical axis, a channel surrounding the tank at its upper end and having an outlet, a member attached to the outer rotor to propel froth on top of the contents of the tank outwardly therefrom and into the channel, and an element operatively connected to the outer rotor and lying within the channel, said element propelling the froth within the channel to the outlet.

9. Apparatus for froth flotation which comprises a tank having a solid bottom which is directly exposed to the interior of the tank and on which solids may collect, a pair of vertical shafts moor-ted for rotation on the same axis and lying one him the other, a rotor connected to each st and lying within the tank, each rotor inc1. mg a circular series of spaced staves and the series lying one within the other and at least one rotor lying close to the bottom of the tank, and means for driving the rotors at different speeds.

10. Apparatus for froth flotation which comprises a tank, a pair of vertical shafts mounted for rotation on the same axis and lying one within the other, a rotor connected to eacr bait and lying within the tank, each rotor inch. mg upper and lower heads connected by a circular series of spaced staves, the series lying one within the other, and means for driving the rotors at different speeds.

11. Apparatus for froth flotation which comprises a tank, a, pair of vertical shafts mounted for rotation on the same axis and lying one within the other, a rotor connected to each shaft and lying within the tank, each rotor including a head and a circular series of spaced staves projecting therefrom, the series lying one within the other, and means for driving the rotors at difierent speeds.

12. Apparatus for froth flotation which comprises a tank, a pair of vertical shafts mounted for rotation on the same axis and lying one within the other, a rotor connected to each shaft and lying within the tank, one rotor including propeller blades and the other a disc overlying said blades and spaced therefrom, and means for driving the rotors at different speeds.

13. Apparatus for froth flotation which comprises a tank having a bottom and a side wall, an inlet for admitting pulp to be treated through the bottom, the bottom being otherwise imperforate and being directly exposed to the interior of the tank, an outlet through the side wall close to the bottom, a pair of rotors mounted for rotation on the same vertical axis within the tank, and means for rotating the rotors at diflerent speeds.

14. Apparatus for froth flotation which comprises a tank having a bottom and a side wall, an inlet for admitting pulp to be treated through the bottom, the bottom being otherwise imperforate and being directly exposed to the interior of the tank, an outlet through the side wall close to the bottom, a pair of rotors mounted for r0- tation on the same vertical axis within the tank, a member'attached to one rotor and terminating close to the bottom of the tank, said member sweeping material along said bottom to the outlet, and means for rotating therotors at diflerent speeds.

LOUIS STEFFEN PETERSEN. 

